A collimating lens can be utilized to direct the light output to a required region. With a light source in the center, the collimating lens can be designed so that it has a focal point in the center. Light emitted from the light source passes through the lens and converges on parallel beams of light at the height of the lens. A typical collimating lens has a plane appearance and may harm the human eye if looking directly at the collimating lens. A Fresnel lens, on the other hand, does the function in a manner similar to that of a collimating lens, but removes the plane appearance in one axis and is less harmful to its counterpart-collimating lens. A Fresnel lens is generally more compact and less expensive than its bulk optic counterpart. The Fresnel lens is also well suited for optical systems that do not require a high wave front quality. One such system is the illumination-portion of a projection system, which gathers as much light as possible from an extended source and directs it onto a pixilated panel.
The Fresnel lens can be configured as a special optical lens made from plastic such as, for example, acrylic, Polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polycarbonate (PC) and High Density Polyethylene (HDPE). Modern Fresnel lenses are often employed as light condensers, illuminators, and magnifiers, and in many other applications. Fresnel lenses basically include a series of concentric prismatic grooves, designed to cooperatively direct incident light rays to a common focus. This type of lens is thin, lightweight, and includes a high aperture. Also, this type of lens can be accurately mass-produced utilizing replication techniques.
Generally, in prior art Fresnel lenses intended for visible light applications, the grooves are all the same width, so that the groove density is constant across the lens. The depth of the grooves increases as the distance between the groove and the center of the lens increases. The depth of the deepest groove places a limit on the minimum thickness of the lens. Therefore, if the depth of the grooves can be reduced, the thickness of the lens can be reduced. Diffraction effects, however, caused by the grooves of the lens provide different path lengths, which can give rise to a destructive interference at the detector, whereby the efficiency of the lens is further impaired.
Referring to FIG. 1 a front view of a prior art Fresnel lens 100 with “V” grooves is illustrated. The prior art Fresnel lens 100 depicted in FIG. 1 includes grooves 110. The Fresnel lens 100 has a front face 130 and a mounting bracket 120. Parallel grooves 110 can be created in between the Fresnel Lens 100 in order to avoid the plain appearance in front of the Lens. Each groove 110 is triangular in cross section and is parallel to each other. The Fresnel lens 100 removes the plane appearance in one axis and is less harmful to its counterpart-collimating lens. Grooves 110 are generally provided as “V” grooves, which reduce the light output at the required area.
Referring to FIG. 2, a perspective view of a Fresnel lens 200 with “V” grooves is illustrated. The Fresnel lens 200 depicted in FIG. 2 possesses a body 130 and a mounting bracket 120. Note that in FIGS. 1-2, identical or similar blocks and elements are generally indicated by identical reference numerals. One surface of the body 130 is flat. The other surface of the body 130 houses the Fresnel lens 200 with a plurality of concentric grooves 110. Other types of prior art lenses possess grooves on both sides. Each groove 110 can contain a side 140, which extends from the surface of the lens 200 to an innermost point 150. It is known in the art that a spherical surface on a lens such as lens 100 and/or 200 can produce a spherical aberration. The grooves 110, however, in the Fresnel lens 200 introduce a scattering effect and refract some of the rays in undesired directions.
Referring to FIG. 3, a prior art graph 300 illustrates a simulation result of a Fresnel lens with “V” grooves. As shown in FIG. 2, the grooves 110 reduce light output at required area. The total light at required location is only four lumens. The prior art Fresnel lens 100 and/or 200 will encounter a difficulty in precisely controlling the light paths. As a result, parallel rays cannot be obtained over the entire surface of the inner Fresnel lens 100/200, and the brightness distribution will be uneven. This is a natural result of a fact that fine optical designing is not performed on the lens steps in accordance with the surface shape of the Fresnel lens 100 or 200.
The portion of the Fresnel lens 100 or 200 that is substantially curved will cause a considerable deviation from the desired brightness distribution due to a contribution of unexpected rays. Designing the prior art Fresnel lens 100 or 200 with grooves 110, however, cannot be obtained easily. Therefore, much time and work are needed to design the Fresnel lens 100/200, and its final design and performance will depend on the experiences of the designer.
Based on the foregoing difficulties, it is apparent that there is a need for an improved cylindrical Fresnel lens with an enhanced diffuser and aesthetic appearance, and which offers the effective usage of light while simultaneously reducing both production and performance costs. It is believed that a solution to these needs is described in greater detail herein.